Skip to main content

Full text of "Text Book Of Mechanical Engineering"

See other formats

Wheel Moulding.                              31

"bolted together; h is a ring to stiffen ^ and / is a pronged plate
to support the core/

The cone pulley B may be struck out in the floor, while the
internal core is made separately on a plate : patterns being used
for webs and boss. In fact, any casting of regular shape, either
circular or cubical, may be moulded in loam much more
•economically than by means of wooden patterns ; the symmetrical
parts being struck, and projecting pieces having core boxes.

A few other examples of moulds in green sand for different
objects, requiring no special description after what has been
previously said, are given in Fig. 44, where A is a stop-valve, the
larger core box for which has a loose pin to form the impression
•needed to support the smaller core : B a large marine- or stationary-
engine piston, the core being supported by and vented through the
pieces aa, which are filled in on finished casting by screwed plugs.
Boxes are needed for the cores cc, and c represents the mould for
a plummer block. (See Appendix //, p. 784.)

"Wheel Moulding.—Not many years ago all spur and bevel
wheels were m.oulded by providing a finished pattern for the
wheel required, but as machine moulding is not only simpler, but
•far more accurate, and as it does away with the necessity for
storing heavy patterns, which are sure to be out of truth by the
next time they ^are- required, toothed wheels are now extensively
moulded by machine.

Scott's wheel moulding machine may be understood by
reference to Fig. 46, and it may be premised that three operations
are necessary in the working of it.

A board B is set upon the central spindle A (see Fig. 45), for
the purpose of striking out the greatest diameter of wheel, on
which the teeth are to be formed, giving at the same time the
height of the top and the bottom of the rim. The spindle being
•removed, the machine is put in the central socket c, Fig. 46, and
the operations are now to be explained.

A pattern D, of two teeth, is accurately made in hardwood,
and being fastened to the upright arm E of the machine, this
.arm needs to be—(i), fixed to the requisite radius of wheel;
(2), raised or lowered; (3), passed round the rim of the wheel
by the rotation of the arm F.